Organic light emitting display (OLED) device with advantages such as self-luminous, low driving voltage, high luminous efficiency, short response time, high definition and contrast, nearly 180° viewing angle, wide temperature range, flexible and large-area panchromatic display, and so on, is recognized as the most promising display device in the industry.
OLED display device generally includes: a substrate, an anode disposed on the substrate, a hole injection layer disposed on the anode, a hole transport layer disposed on the hole injection layer, a light-emitting layer disposed on the hole transport layer, an electron transport layer disposed on the light-emitting layer, an electron injection layer provided on the electron transport layer, and a cathode provided on the electron injection layer. The light-emitting principle of OLED display devices is that semiconductor materials and organic light-emitting materials being driven by an electric field to emit light by carrier recombination. Specifically, the OLED display device usually adopts indium tin oxide (ITO) pixel electrodes and metal electrodes as the anode and the cathode of the device, respectively. Under a certain driving voltage, electrons and holes are injected from the cathode and the anode into the electron transport layer and the holes transport layer, the electron and the hole respectively migrate to the light-emitting layer through the electron transport layer and the hole transport layer, and meet in the light-emitting layer to form an exciton and excite the light-emitting molecule, which emits visible light through radiation relaxation.
The OLED display device can be classified into passive matrix OLED (PMOLED) type and active matrix OLED (AMOLED) type according to driving modes, that is, direct addressing and thin film transistor (TFT) matrix addressing two categories. Among them, AMOLED has matrix arranged pixels, belonging to the active display type, which has high luminous efficiency and usually being used for high-definition large-size display device.
AMOLED is a current-driven device. When a current flows through the organic light-emitting diode, the organic light-emitting diode emits light, and the light-emitting brightness is determined by the current flowing through the organic light-emitting diode itself. Most of the existing integrated circuits (ICs) only transmit voltage signals, so the pixel driving circuit of AMOLED needs to complete the task of converting voltage signals into current signals. Generally, the AMOLED pixel driving circuit is provided with a driving thin film transistor for driving the organic light emitting diode to emit light. In use, due to the aging of the organic light emitting diode and the threshold voltage variation of the driving thin film transistor, display quality of the OLED display device will decrease. Accordingly, in the prior art, the sub-pixels of the OLED display device are electrically connected to a detection chip (IC) through a plurality of sensing lines. The detection chip inputs a reference voltage to the plurality of sub-pixels via the plurality of sensing lines, meanwhile detecting the sub-pixels to acquire the degree of aging of the organic light emitting diodes and the threshold voltage variation degree of the driving thin film transistors, and thereby to compensate the aging of the organic light emitting diodes and the threshold voltage variation, so as to ensure the display quality of the OLED display device.
Please refer to FIG. 1, which is a schematic structural diagram of an existing OLED display device. The OLED display device includes an OLED panel 100′, a detection chip 200′ and a plurality of sensing lines 300′ electrically connecting the detection chip 200′ to the OLED panel 100′. The detection chip 200′ has a linear internal wiring 210′ and a plurality of switches S′ respectively corresponding to the sensing lines 300′. Each of the sensing lines 300′ is electrically connected to the internal wiring 210′ through the corresponding switches S′. Two ends of the internal wiring 210′ are electrically connected to one end of an external input wiring 400′, respectively, the other ends of the two external input wirings 400′ are accessing to a reference voltage, Vref. A plurality of switches S′ are turned off during operation, the reference voltage inputs into the plurality of sensing lines 300′ through the external input wiring 400′ and the internal wiring 210′, respectively, and then inputs into the OLED panel 100′. Since both the internal wiring 210′ and the external input wiring 400′ have equivalent resistances, and current flows through the sensing lines 300′, the internal traces 210′, and the external input wiring 400′ when the OLED display device is operating, IR drop effect with different degrees is generated at different positions of the internal wiring 210′. Moreover, the positions of the plurality of sensing lines 300′ electrically connected to the internal wiring 210′ are different, that may cause voltage variation between the reference voltage and the voltage inputted to different sensing lines 300′ via the detection chip 200′, wherein the middle part of the sensing line 300′ has the most serious reference voltage variation. In order to improve the display quality of the picture and eliminate the voltage variation when the reference voltage inputted to the different sensing lines 300′ due to the IR voltage drop effect of the internal wiring 210′, the prior art generally increases the area of the internal wiring 210′ to reduce the equivalent resistance of the internal wiring 210′, however, the size of the detection chip 200′ is greatly increased.